Technologies to harness solar energy can be divided broadly into (a) those that convert sunlight to electricity, and (b) those that convert sunlight to heat, which may in turn either be used to generate electricity or be used to heat water or heat living spaces, for example. Photovoltaic systems are an example of technology that converts sunlight into electricity by using solar cells whose electrical characteristics change when exposed to sunlight. Solar thermal collectors are an example of technology that converts sunlight into heat, by absorbing sunlight and transferring resultant heat into water or another working fluid which circulates through the solar thermal collector.